In general, air cleaner arrangements include a housing and an air filter element. The housing is configured such that air is directed through the air filter element, for filtering. Various geometric configurations of the air cleaner housing, the air filter element, and related seal arrangements are used to effect this.
Many air cleaner arrangements include generally cylindrical air filter elements. Such elements typically include filter media arranged in a cylindrical pattern, with end caps. Seal arrangements are used either on or in conjunction with the end caps, to provide appropriate sealing with the housing or other portions of the air cleaner, and to control the direction of air flow.
Reverse air flow air cleaner arrangements are generally those in which air is directed to an interior of the air filter element before it is filtered, and the air is filtered as it passes through the air filter element from the interior to the exterior. If the air filter element is cylindrical, this means that the unfiltered air is directed into the interior of the cylinder, and then through the filter media, to an exterior, during filtering. Material entrained in the air directed into the air filter, then, is left along an interior of the cylindrical filter media.
Consider for example, a reverse flow air cleaner arrangement, having a cylindrical air filter element, utilized on an over the highway truck. Air directed into the interior of the cylindrical element may include dust, leaves, large particulates, and even moisture entrained therein. This material will tend to build up in the interior of the air filter element, in time. If the water depth inside the air filter becomes significant, the water, alone or with fine particulates or salt in suspension, can permeate filter media. This has the potential to damage engine components. It is would be preferred that arrangements be provided to drain the water from the interior of the filter element.
In those arrangements wherein the filter element is operationally oriented such that the longitudinal axis of the cylindrical air filter is substantially vertical, drainage arrangements involving drainage apertures in one of the end caps have been used. In general, these have involved offset (from a central location) apertures in one end cap, and unless the air filter element is oriented nearly perfectly vertically, drainage is inefficient. Also, in such arrangements debris can sometimes collect along interior surfaces of the housing when the arrangement is opened and the element is removed; and, unless the housing is thoroughly cleaned before the element is reinserted into the housing, the debris can interfere with attainment of a good seal at critical locations.